Method and device for coating adhesive surfaces of fixing elements with a hot-melt adhesive

ABSTRACT

The invention relates to a method for coating adhesive surfaces of fixing elements with a hot-melt adhesive and to a device for carrying out said method.

The invention relates to a method for coating adhesive surfaces offixing elements with a hot-melt adhesive and to a device for carryingout said method.

This specifically involves the application of highly reactive hot-meltadhesives, which are designed to be wear-resistant and non-adhesive attemperatures up to 50° C., and which can be reactivated by means of heator the supplying of another kind of energy in order to produce apermanent adhesive bond. In conjunction with that, the applied adhesivelayer must be absolutely adhesion-proof or adhesion resistant until thecomponent or carrier elements are used, and should not release theadhesive force inherent in the adhesive until the reactivating of theadhesive at the usage site.

It is already known from WO 98/18612 that for the coating of adhesivesurfaces of fixing elements, the pre-mixed hot-melt adhesive in solid,preferably powder form, can be applied to the adhesive surface and canthen be exposed to a thermal effect sufficient to adhere the adhesive byexerting a pressing force. Doing this depends on the fact that the fulladhesive surface is coated with a uniformly thin layer and is thenpressed with a stamp having a surface that is aligned absolutelyparallel to the adhesive surface. This coating method is conceived morefor the coating of small quantities, e.g., in an experimentallaboratory, and is only designed for the coating of simply configured,flat adhesive surfaces such as the collar plates of fastening bolts.

The task of the invention is to make this known adhesive joining methodusable for fixing elements with complex adhesive surfaces as well, andto develop a fully automatic method operation and to configure thedevice for carrying out this method in such a way that even fixingelements with uneven adhesive surfaces can be coated uniformly.

According to the present invention, this task is solved essentiallythrough the following method steps indicated in claim 1:

-   -   The adhesive powder is first filled into recesses in a working        plate having contours that correspond to the adhesive surface of        the fixing element, and is then smoothed out in the desired        thickness,    -   after previously being heated in a heating station to the        temperature required for adhesion, the fixing element is        deposited over the recesses that have been filled with the        powdered adhesive,    -   the adhesive powder is then pressed against the adhesive surface        from below by tappets having a cross section that is matched to        the recesses and top sides that are matched to the geometry of        the fixing element.

A device for carrying out the method according to the invention ischaracterized by the following features according to claim 2:

-   -   It possesses a working plate with recesses corresponding to the        contours of the adhesive surface of the fixing element,    -   the base surfaces of the recesses are formed by tappets, which        have lateral walls that are displaceably guided within the        recesses and the top side of which is matched in form to the        geometry of the fixing element,    -   arranged laterally to the recesses on the working plate is a        horizontally displaceable container for filling the adhesive        powder into the recesses, whereby the side edges of the        container sweep flush over the working plate,    -   arranged on the other side of the recesses is a sliding plate,        also horizontally displaceable, which is used for receiving the        fixing element and which is provided with continuous holes for        the tappets that rise up from the working plate,    -   arranged over the recesses is a vertically displaceable pressure        stamp with a pressure plate that is lowered onto the fixing        element,    -   installed at a distance from the sliding plate is a heating        station that brings the fixing elements to the desired heating        temperature before they are transported over the recesses.

Additional features of the invention can be found in the subclaims andin the following description of embodiments of the invention that areshown in the drawings. The following are shown:

FIG. 1 The schematic representation of a device for carrying out theinventive coating a)-f) method with the successive method steps,

FIG. 2 A perspective view of a holder for rain sensors with inventivelycoated hot-melt adhesive for adhesion onto an uneven windshield,

FIG. 3 The bottom view of the same holder with a view towards theadhesive surfaces,

FIG. 4 A section through the holder along the line IV-IV in FIG. 3,

FIG. 5 The schematic representation of a section through the workingplate, the sliding plate with an inserted holder per FIG. 4, and thehot-melt adhesive-filled recess before the tappets are raised,

FIG. 6 The same section after the tappets have been raised,

FIG. 7 A perspective view of a holder with a ball joint pivot foradhesion to an uneven automobile rear window,

FIG. 8 The same holder in a bottom view with two broad adhesivesurfaces,

FIG. 9 A schematic representation of a section through the workingplate, the sliding plate with an inserted holder, and the hot-meltadhesive-filled recess with three adjacent displaceable tappets beforethey are raised, and

FIG. 10 The same sectional representation after the tappets have beenraised.

The device shown in FIG. 1 is used for carrying out the inventive methodfor coating the adhesive surfaces of fixing or holding elements withhot-melt adhesive. It is comprised of a working plate 1 that is providedwith recesses 2 corresponding to the contours of the adhesive surface 3of the fixing element 4. In conjunction with that, the base surfaces 5of the recesses 2 are formed by tappets 6, the lateral walls 7 of whichare displaceably guided in the recesses 2. The top side 8 of the tappets6 is matched in form to the adhesive surface 3 of the fixing element 4;this means that it is not only matched to the contours of the adhesivesurfaces 3, but that it is also configured absolutely parallel to theadhesive surface 3.

Arranged laterally next to the recesses 2 on the working plate 1 is acontainer 9 for filling the adhesive powder into the recesses 2. Thiscontainer 9 is guided in a horizontally displaceable manner on theworking plate 1, whereby the side edges 10 of the container 9 sweepflush over the working plate 1.

In addition, arranged on the other side of the recesses 2 is a slidingplate 11 which is used for receiving the fixing or holding element 4 andwhich is also guided in a horizontally displaceable manner on theworking plate 1 in the direction towards the recesses 2. In conjunctionwith that, the top side of this sliding plate 11 is matched in form tothe geometry of the adhesive surfaces 3. This sliding plate 11 isprovided with continuous holes 12 which are for the tappets 6 that riseup from the working plate 1 and the inner walls of which are alsomatched in form to the lateral walls 7 of the tappets 6.

Arranged over the recesses 2 is a vertically displaceable pressure stamp13 with a pressure plate 14 that is lowered onto the fixing element 4that has been inserted into the sliding plate 11. In addition, arrangedat a distance from the sliding plate 11 is a heating station 15 thatheats the fixing elements 4 to the desired melting temperature beforethey are transported over the recesses 2.

The operating sequence shown in FIGS. 1 a) through f) can be describedas follows:

FIG. 1 a) The container 9 and the sliding plate 11 are located in theirstarting position next to the recess 2 on the working plate 1, thepressure plate 14 in its upper waiting position and the tappets 6 withtheir top sides 8 below the plate level.

FIG. 1 b) The fixing element 4 is located above the heating station 15,which is installed at a distance from the sliding plate 11, and isheated there to the desired melting temperature. At the same time, thecontainer 9 with the powder adhesive is moved above the recesses 2 tothe right in the direction of the arrow in order to fill them withpowder. The container 9 is then moved back again, whereby the side edges10 of the container 9 sweep flush over the working plate 1 and at thistime draw the powder off into the recess 2 to the desired fillingheight.

FIG. 1 c) The preheated fixing element 4 is placed next to the recesses2 on the sliding plate 11, the top side of which is matched in form tothe geometry of the adhesive surface 3.

FIG. 1 d) The sliding plate 11 with the inserted fixing element 4 ismoved over the recesses 12, and specifically, in such a way thatcontinuous holes 12 align with the tappets 6.

FIG. 1 e) The pressure plate 14 is lowered onto the fixing element 4. Atthe same time, the tappets 6 are raised from below through thecontinuous holes 12, and the adhesive powder that has been prepared inthe recesses 2 is pressed against the underside of the heated fixingelement 4.

FIG. 1 f) After the fixing element 4, preheated at the heating station,has been exposed to a thermal effect sufficient to adhere the adhesive,the pressure plate 14 is raised again and the sliding plate 11 is movedback to the side. The coated fixing element 4 can then be lifted fromthe sliding plate 11 and stored in a container, not shown in thedrawing.

The fixing element shown in FIGS. 2 through 4 is a holder for rainsensors that are to be adhered to uneven windshields. This holder iscomprised of a rectangular frame 16 with fastening locations 17 for thesensors, not shown, formed onto the four corners, and two laterallyopposed projecting holding tabs 18 for gripping the frame 16. Providedon the underside of the frame 16 on the longitudinal sides 19 andtransverse sides 20 are adhesive surfaces 21 and 22, which are coatedwith a thin layer of hot-melt adhesive in accordance with the invention.

FIG. 5 shows a schematic representation of the frame 16 of the holdershown in FIGS. 2 through 4 lying on the sliding plate 11, withhorizontal longitudinal sides 19 and, at an angle to same, transversesides 20, which are located above the recesses 2 and the continuousholes 12 and which are pressed down onto the sliding plate 11 from aboveby the pressure plate 14. In conjunction with that, the recesses 2 havepreviously been filled with adhesive powder from the container 9 on thetop side 8 of the tappet 6 and then swept smooth to the level of thesurface of the working plate 1 by the side edge 10 of the container 9.

In the same schematic representation, FIG. 6 shows the way in which theadhesive powder is pressed and compressed plane-parallel against theadhesive surfaces 22 of the transverse sides 20 by the tappets 6 afterthey have been raised, until the powder has melted as a result of thecontact with the preheated frame 16 and adheres to the adhesivessurfaces 22 as a result of the pressing force generated by the tappets6.

The embodiment represented in FIGS. 7 through 10 shows another holderwith a ball pivot 26 to be adhered to the uneven surface of anautomobile rear window. In this regard, the ball pivot 26 is used tobear a so-called gas spring which is borne at the other end on thewindow frame and which supports the rear window after it has been swungup. This holder is comprised of a kidney-shaped base plate 23 with anangled ball pivot 26 at the central plate section 24, and adhesivepowder-coated, broad adhesive surfaces 25 configured on the opposingends. The latter are inclined at a slight angle to the central platesection 24, and are matched to the rear window surface which is inclinedat the same angle.

As can be seen from the schematic representation of a section throughthe working plate 1 in FIGS. 9 and 10, each of the base surfaces 5 ofthe recesses 2 in the present embodiment is formed by three tappets 27,28 and 29 in the working plate 1, which are displaceable relative to oneanother and which are held by a tappet retaining plate 33. Inconjunction with this, the top sides 30, 31 and 32 of each tappet 27, 28and 29 are matched in form to the particular associated partial areas 25a), 25 b) and 25 c) of the adhesive surfaces 25.

In the starting position shown in FIG. 9, the top sides 30, 31 and 32 ofthe tappets 27, 28 and 29 form three levels that are stepped relative toone another, whereby the particular upper ends of the top sides lie atthe same height. What is accomplished by doing this is that in thestarting position, the layer thickness of the filled adhesive powderfluctuates only slightly over the width of the tappets 27, 28 and 29.

FIG. 10 shows the same sectional representation after the tappets 27, 28and 29 have been raised. In conjunction with this, the difference inlevels among the tappet top sides 30, 31 or 32 is compensated forthrough the fact that the tappets are slightly staggered relative to oneanother until they all lie in a single plane against the adhesivesurfaces 25 a), b) and c) so that a uniformly thick layer of adhesivepowder is applied compressed onto the adhesive surface 25.

1. Method for coating adhesive surfaces of fixing elements with hot-meltadhesive, whereby the pre-mixed adhesive in pulverized form is appliedto the adhesive surface and is exposed to a thermal effect sufficient toadhere the adhesive by exerting a pressing force, characterized in thatthe adhesive powder is filled into recesses in a working plate havingcontours that correspond to the adhesive surface of the fixing element,and is then smoothed out in the desired thickness, after previouslybeing heated to the temperature required for adhesion to the adhesivesurfaces, the fixing element is deposited over the recesses that havebeen filled with the powdered adhesive, the adhesive powder is thenpressed against the adhesive surfaces from below by tappets having across section that is matched to the recesses and top sides that arematched to the geometry of the adhesive surfaces.
 2. Device for carryingout the coating method according to claim 1, comprised of a workingplate (1) with recesses (2) corresponding to the contours of theadhesive surface (3) of the fixing element (4), whereby the basesurfaces (5) of the recesses (2) are formed by tappets (6), which havelateral walls (7) that are displaceably guided within the recesses (2)and the top sides (8) of which are matched in form to the geometry ofthe adhesive surfaces (3), arranged laterally on the working plate (1),a horizontally displaceable container (9) for filling the adhesivepowder into the recesses (2), whereby the side edges (10) of thecontainer (9) sweep flush over the working plate (1), arranged on theother side of the recesses (2), a sliding plate (11), also horizontallydisplaceable, which is used for receiving the fixing element (4) andwhich is provided with continuous holes (12) which are for the tappets(6) that rise up from the working plate (1) and the inner walls of whichare matched to the lateral walls (7) of the tappets (6), arranged overthe recesses (2), a vertically displaceable pressure stamp (13) with apressure plate (14) that is lowered onto the fixing element (4), and,installed at a distance from the sliding plate (11), a heating station(15) for heating the fixing elements (4) to the desired heatingtemperature before they are transported over the recesses (2).
 3. Devicefor carrying out the coating method according to claim 2, whereby thefixing element is comprised of a base plate (23) with adhesive surfaces(25) of greater width configured on both sides of the central platesection (24), and these adhesive surfaces (25) exhibit a geometry thatdiffers from that of the central plate section (24), characterized inthat each of the base surfaces (5) of the recess (2) is formed by two ormore tappets (27), (28) and (29) which are displaceable relative to oneanother, whereby the top sides (30) (31) (32) of each tappet (27) (28)(29) are matched in form to the particular associated geometry of thepartial areas (25 a) (25 b) (25 c) of the adhesive surfaces (25). 4.Device for carrying out the coating method according to one of theclaims 2, characterized in that the top side of the sliding plate (11)is matched in form to the geometry of the adhesive surfaces (3), (21 and22) and (25).
 5. Device for carrying out the coating method according toone of the claim 3, characterized in that the top side of the slidingplate (11) is matched in form to the geometry of the adhesive surfaces(3), (21 and 22) and (25).